1. Field of the Invention
This invention relates to a process of needling a non-woven strip to a revolving endless carrier web, wherein the non-woven strip is fed at a predetermined lead angle and is applied to the carrier web to form a plurality of convolutions at least in one ply and is continually needled to the carrier web and the position and longitudinal direction of the convolution which has been needled to the carrier web during the preceding revolution thereof is utilized for a control of the traversing movement of the non-woven strip as it is applied to the carrier web in dependence on the desired lead angle. The invention relates also to an apparatus for carrying out the process.
2. Description of the Prior Art
When it is desired to apply to a usually endless revolving endless carrier web a non-woven strip in such a manner that the non-woven strip, which is fed to the carrier web by a suitable feeder, can be laid on the carrier web in the longitudinal direction of that last preceding convolution of the non-woven strip on the carrier web, it will be necessary to detect the position and longitudinal direction of that convolution of the non-woven strip which has been applied to the carrier web during its last preceding revolution so that the feeder for the non-woven strip can be moved to a corresponding extent transversely to the direction of travel and longitudinal direction of the carrier web. Because the step formed in the surface of the carrier web by the needled-on non-woven strip is small owing to the small thickness of the needled-on non-woven web and because the non-woven strip has only a low-strength, excessive errors would be involved in a mechanical or non-contacting scanning of the free longitudinal edge of that last preceding convolution of the non-woven strip on the carrier web. For this reason it has already been proposed (EP-A-123 969) to provide an optoelectronic monitoring device including a line-scanning camera for detecting a marking thread which is applied to the carrier web concurrently with the non-woven strip and has a suitable contrasting color. The position of that marking thread can readily be detected by the line-scanning camera and can be used for a control of the traversing movement of the feeder for the non-woven strip relative to the carrier web.
But that known process has the disadvantage that the position and longitudinal direction of the non-woven strip can be detected only by a detection of the marking thread which has been applied to the carrier web concurrently with the non-woven strip whereas it is not possible to detect the position and direction of the free longitudinal edge of the last preceding convolution formed by the non-woven strip so that variations of the width of the non-woven strip cannot be taken into account. As a result, an application of the several convolutions of the non-woven strip with closely adjoining edges or with a predetermined, constant overlap can be accomplished only with great difficulty in practice. Besides, any irregularities of the laying of the marking thread will be reflected by the control so that the application of the marking thread may constitute a cause of additional errors in the exact laying of the several convolutions of the non-woven strip. Finally, the application of a marking thread which is concurrent with the non-woven strip to the carrier web involves a higher expenditure because such marking thread must usually be removed from the carrier web before a new convolution of the non-woven strip is applied to the carrier web.